<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    *{
        padding: 0;
        margin: 0;
        box-sizing: border-box;
    }
    .box{
        overflow: hidden;
        background: #ccc;
        padding: 20px;
        height: 300px;
    }
    .left{
        width: 200px;
        height: 300px;
        float: left;
        background: seagreen;
    }
    .right{
        width: 200px;
        height: 300px;
        float: right;
        background: seagreen;
    }
    .middle{
        background: pink;
        height: 300px;
        margin: 0 220px;
    }

    .wrap{
        height: 100px;
    }
    .wrap>div{
        background: skyblue;
        width: 200px;
        height: 100px;
    }
    .left1{
        float: left;
    }
    .right1{
        float: right;
    }
    .center{
        
        margin: 0 auto;
    }

</style>
<body>
    <div class="box">
        <div class="left">左边</div>
        <div class="right">右边</div>
        <!-- 左右浮动的时候，把中间的元素 放到最下面 不能放中间 -->
        <div class="middle">中间</div>
    </div>


    <div class="wrap">
        <div class="left1">1</div>
        <div class="right1">2</div>
        <div class="center">3</div>
    </div>
</body>

</html>